This paper described acetone sensing using ZnO based Film Bulk Acoustic Resonator (FBAR). The resonant frequency of the FBAR increased as the concentration of acetone increased. The detection limit of acetone was around 4 ppm. The density decrease of the ZnO induced by releasing carbon dioxide generated from the reaction between acetone and the adsorbed oxygen ions on the ZnO surface was assumed to be responsible for the frequency upshift. Upon exposure to ethanol (a major environmental crosstalk for traditional acetone sensors), an opposite response (decrease of resonant frequency) was observed. Water was generated and absorbed on the ZnO surface during the ethanol sensing process. Thus, the density of the ZnO film increased, resulting in a frequency drop. FBAR sensor possessed the unique ability to distinguish acetone from ethanol due to their different reaction behaviors.